From 769cfb81a222c842c40085723c05a8b5c853427f Mon Sep 17 00:00:00 2001
From: Jody Klymak <jklymak@gmail.com>
Date: Tue, 13 Mar 2018 10:21:11 -0700
Subject: [PATCH 1/2] API: check locator and formatter args when passed

---
 lib/matplotlib/axis.py              | 12 ++++++++++++
 lib/matplotlib/tests/test_ticker.py | 24 ++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
index b15e5af483dc..220af0f6529a 100644
--- a/lib/matplotlib/axis.py
+++ b/lib/matplotlib/axis.py
@@ -1568,6 +1568,9 @@ def set_major_formatter(self, formatter):
 
         ACCEPTS: A :class:`~matplotlib.ticker.Formatter` instance
         """
+        if not hasattr(formatter, 'format_data'):
+            raise TypeError("formatter argument should be instance of "
+                    "matplotlib.ticker.Formatter")
         self.isDefault_majfmt = False
         self.major.formatter = formatter
         formatter.set_axis(self)
@@ -1579,6 +1582,9 @@ def set_minor_formatter(self, formatter):
 
         ACCEPTS: A :class:`~matplotlib.ticker.Formatter` instance
         """
+        if not hasattr(formatter, 'format_data'):
+            raise TypeError("formatter argument should be instance of "
+                    "matplotlib.ticker.Formatter")
         self.isDefault_minfmt = False
         self.minor.formatter = formatter
         formatter.set_axis(self)
@@ -1590,6 +1596,9 @@ def set_major_locator(self, locator):
 
         ACCEPTS: a :class:`~matplotlib.ticker.Locator` instance
         """
+        if not hasattr(locator, 'tick_values'):
+            raise TypeError("formatter argument should be instance of "
+                    "matplotlib.ticker.Locator")
         self.isDefault_majloc = False
         self.major.locator = locator
         locator.set_axis(self)
@@ -1601,6 +1610,9 @@ def set_minor_locator(self, locator):
 
         ACCEPTS: a :class:`~matplotlib.ticker.Locator` instance
         """
+        if not hasattr(locator, 'tick_values'):
+            raise TypeError("formatter argument should be instance of "
+                    "matplotlib.ticker.Locator")
         self.isDefault_minloc = False
         self.minor.locator = locator
         locator.set_axis(self)
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
index 32206a0c6168..da2227e6805f 100644
--- a/lib/matplotlib/tests/test_ticker.py
+++ b/lib/matplotlib/tests/test_ticker.py
@@ -728,3 +728,27 @@ def test_latex(self, is_latex, usetex, expected):
         fmt = mticker.PercentFormatter(symbol='\\{t}%', is_latex=is_latex)
         with matplotlib.rc_context(rc={'text.usetex': usetex}):
             assert fmt.format_pct(50, 100) == expected
+
+
+def test_majformatter_type():
+    fig, ax = plt.subplots()
+    with pytest.raises(TypeError):
+        ax.xaxis.set_major_formatter(matplotlib.ticker.LogLocator())
+
+
+def test_minformatter_type():
+    fig, ax = plt.subplots()
+    with pytest.raises(TypeError):
+        ax.xaxis.set_minor_formatter(matplotlib.ticker.LogLocator())
+
+
+def test_majlocator_type():
+    fig, ax = plt.subplots()
+    with pytest.raises(TypeError):
+        ax.xaxis.set_major_locator(matplotlib.ticker.LogFormatter())
+
+
+def test_minlocator_type():
+    fig, ax = plt.subplots()
+    with pytest.raises(TypeError):
+        ax.xaxis.set_minor_locator(matplotlib.ticker.LogFormatter())

From a6651fee85f8819c56b76cb8b52d1ae234702871 Mon Sep 17 00:00:00 2001
From: Jody Klymak <jklymak@gmail.com>
Date: Tue, 13 Mar 2018 19:19:20 -0700
Subject: [PATCH 2/2] FIX: back to isinstance

---
 lib/matplotlib/axis.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
index 220af0f6529a..406ae8675200 100644
--- a/lib/matplotlib/axis.py
+++ b/lib/matplotlib/axis.py
@@ -1568,7 +1568,7 @@ def set_major_formatter(self, formatter):
 
         ACCEPTS: A :class:`~matplotlib.ticker.Formatter` instance
         """
-        if not hasattr(formatter, 'format_data'):
+        if not isinstance(formatter, mticker.Formatter):
             raise TypeError("formatter argument should be instance of "
                     "matplotlib.ticker.Formatter")
         self.isDefault_majfmt = False
@@ -1582,7 +1582,7 @@ def set_minor_formatter(self, formatter):
 
         ACCEPTS: A :class:`~matplotlib.ticker.Formatter` instance
         """
-        if not hasattr(formatter, 'format_data'):
+        if not isinstance(formatter, mticker.Formatter):
             raise TypeError("formatter argument should be instance of "
                     "matplotlib.ticker.Formatter")
         self.isDefault_minfmt = False
@@ -1596,7 +1596,7 @@ def set_major_locator(self, locator):
 
         ACCEPTS: a :class:`~matplotlib.ticker.Locator` instance
         """
-        if not hasattr(locator, 'tick_values'):
+        if not isinstance(locator, mticker.Locator):
             raise TypeError("formatter argument should be instance of "
                     "matplotlib.ticker.Locator")
         self.isDefault_majloc = False
@@ -1610,7 +1610,7 @@ def set_minor_locator(self, locator):
 
         ACCEPTS: a :class:`~matplotlib.ticker.Locator` instance
         """
-        if not hasattr(locator, 'tick_values'):
+        if not isinstance(locator, mticker.Locator):
             raise TypeError("formatter argument should be instance of "
                     "matplotlib.ticker.Locator")
         self.isDefault_minloc = False